The present invention relates to an ultraviolet-absorbing (UV-absorbing) filter which absorbs an ultraviolet component (UV component) of incoming light to reduce the amount of the UV component of transmitted light and an optical apparatus, such as a light source system, an illuminating optical system, and a projection display apparatus, incorporating the same.
Generally, a projection display apparatus (projector) projects an image displayed on a light valve onto a screen by directing light emitted from a discharge lamp onto the light valve. From the discharge lamp, however, the ultraviolet light (UV light) which degrades the light valve is emitted together with the visible light. The Japanese Patent Publication No. 2,833,055 proposes a method of reducing the amount of an output UV component by coating the cover glass of the reflector in the light source system with multiple layers of a dielectric material that reflect the UV light.
The multiple coats of the dielectric material, however, reflect not only the UV light but also a certain amount of visible light and infrared light (IR light) , and the return light causes the tube temperature of the discharge lamp to increase, thereby promoting devitrification of the silica glass forming the tube and consequently reducing the life of the lamp.
A UV-absorbing glass plate might be used to reduce the return light, thereby decreasing the amount of a UV component of the transmitted light. However, because the discharge lamp, such as a xenon lamp, a metal halide lamp, and a mercury lamp, used as a light source of a projector emits a great amount of UV light, the heat generation associated with the absorption of the UV light can crack (or can melt or burn) the UV-absorbing glass plate, therefore it has been difficult to use the UV-absorbing glass plate in the projector.
It is an object of the present invention to provide a UV-absorbing filter which can reduce the amount of UV component of transmitted light by absorbing the UV component of incoming light, has a high heat dissipation property, and offers a UV-absorbing filter.
According to one aspect of the present invention, a UV-absorbing filter which absorbs a UV component of incoming light to reduce an amount of the UV component of transmitted light, comprising a transparent UV-absorbing glass plate which has a first surface and a second surface and which contains a UV-absorbing substance; a transparent first heat-resistant glass plate which faces the first surface; a transparent second heat-resistant glass plate which faces the second surface; a first distance piece which is made of heat-resistant resin and which is interposed between the first surface and the first heat-resistant glass plate, in the vicinity of an outer edge of the UV-absorbing glass plate, so as to form a first space between the first surface and the first heat-resistant glass plate; and a second distance piece which is made of heat-resistant resin and which is interposed between the second surface and the second heat-resistant glass plate, in the vicinity of the outer edge of the UV-absorbing glass plate, so as to form a second space between the second surface and the second heat-resistant glass plate.
A major constituent of the UV-absorbing glass plate may be potash-lime glass. Further, the UV-absorbing substance contained in the UV-absorbing glass plate may be cerium. Furthermore, the first heat-resistant glass plate and the second heat-resistant glass plate may be made of borosilicate glass. Moreover, the first distance piece and the second distance piece may be made of polyimide. In addition, thicknesses of the first distance piece and the second distance piece may be within a range of 100 xcexcm to 150 xcexcm. Further, the outer edge of the UV-absorbing glass plate, outer edges of the first and second distance pieces, and outer edges of the first and second heat-resistant glass plates may be kept in alignment with one another. Furthermore, the first space is hermetically sealed by the UV-absorbing glass plate, the first heat-resistant glass plate, and the first distance piece; and the second space is hermetically sealed by the UV-absorbing glass plate, the second heat-resistant glass plate, and the second distance piece.
According to another aspect of the present invention, an optical apparatus comprises a lamp; a reflector which reflects light emitted from the lamp; and a UV-absorbing filter disposed on an optical path of the light emitted from the lamp and reflected by the reflector. The UV-absorbing filter includes a transparent UV-absorbing glass plate which has a first surface and a second surface and which contains a UV-absorbing substance; a transparent first heat-resistant glass plate which faces the first surface; a transparent second heat-resistant glass plate which faces the second surface; a first distance piece which is made of heat-resistant resin and which is interposed between the first surface and the first heat-resistant glass plate, in the vicinity of an outer edge of the UV-absorbing glass plate, so as to form a first space between the first surface and the first heat-resistant glass plate; and a second distance piece which is made of heat-resistant resin and which is interposed between the second surface and the second heat-resistant glass plate, in the vicinity of an outer edge of the UV-absorbing glass plate, so as to form a second space between the second surface and the second heat-resistant glass plate.
A reflecting surface of the reflector may have the form of a paraboloid of revolution; and the lamp may be disposed in such a manner that a center of light emission of the lamp is placed in the vicinity of a focal point of the reflector. Further, the optical apparatus may satisfy 1.1 fp less than D/d less than 2.1 fp where a symbol D denotes an opening diameter of the reflector and a symbol d denotes a diameter of the UV-absorbing filter. Furthermore, the optical apparatus may further comprise a condenser lens system which converges the light which has passed the UV-absorbing filter; and a body tube which holds the UV-absorbing filter and the condenser lens system. Moreover, the optical apparatus may further comprise a condenser lens system which converges the light which has passed the UV-absorbing filter, wherein the optical apparatus satisfies 5.1 fp less than fc less than 9.6 fp where a symbol fp denotes a focal length of the reflector and a symbol fc denotes a composite focal length of the condenser lens system. In addition, the optical apparatus may further comprise: an optical pillar element; a light valve; a light transmitting optical system which provides a substantially conjugate relationship between an end of radiation of the optical pillar element and the light valve, the light transmitting optical system directing the light which is converged by the condenser lens system and passes the optical pillar element onto the light valve; and a projection lens system which projects light which has been modulated by the light valve onto a screen.